It is well known in detergent art to formulate bleaching materials in particulate form, as this considered a convenient form for inclusion in many detergent compositions.
In order to obtain good cleaning performance on bleachable stains, e.g. tea, it is desirable to include a bleach material in detergent compositions which are to be used to remove such stains. In dishwashing, especially automatic dishwashing it is well recognised that performance on bleachable stains is one of the key attributes by which consumers assess the effectiveness of a detergent compositions. However, it is well known in the art that the presence of a bleach material in a detergent composition can lead to instability of the composition especially when bleach-sensitive ingredients such as enzymes and perfumes are present. Furthermore the bleach material is generally susceptible to stability problems e.g. when in contact with moisture and/or above ambient temperatures which can typically result in a loss of performance of the bleach material.
These problems have been dealt with in the prior art by physically separating the unstable components from the rest of the composition. Sometimes this has been by providing separate layers of detergent (for example in a tablet) or compartments where different layers contain different parts of the whole composition, thus separating out components that may react with each other. Alternatively the sensitive materials can be coated with a protective layer that prevents interaction with other components of the composition. Or advantageously, both methods used in combination, for added stability and performance.
EP-A-1,735,422 and EP-A-1,735,423 discloses a coated bleaching agent particle consisting of a core containing a bleaching active ingredient, especially a peroxocarboxylic acid, with a coat of water soluble material surrounding this core (such as PVOH).
EP-A-1,633,468 discloses a method for preparing capsules containing at least one imidoperoxycarboxylic acid by applying an inorganic salt onto the at least one imidoperoxycarboxylic acid in particulate form so that the salt forms a capsule shell around the acid.
EP-A-1,633,471 discloses a method for preparing multi-layer capsules containing at least one peroxocarboxylic acid (especially imidoperoxycarboxylic acid) by applying at least two different coating layers each based on at least one polyelectrolyte and/or ionic surfactant.
WO 2004/081161 discloses bleach (PAP) encapsulated with a water soluble coating such as gelatin. This bleach containing capsule is disclosed in combination with a liquid composition inside a water soluble outer container.
Manufacturers have made use of the necessity of multi-compartment or multilayer nature of solid detergent compositions to improve the aesthetics of the compositions by providing the different parts or layers in different shapes and colours.
The colour in the composition is provided through the use of chemical dyes. A particular problem that still remains is to effectively colour the portion of the composition that contains the bleaching compound or material. Bleaches, by their very nature, react with chemical dyes and reduce their colour.
On storage, this leads to the colour of the layer fading. This can also be patchy with the colour becoming uneven, more faded in some places than in others. This effect is undesirable as it reduces the aesthetic appeal of the tablet in the eye of the consumer. This is because makes the tablet appear old and less effective. In fact, this interaction does reduce the effectiveness of the tablet composition, at least in part, as a portion of the bleach has already been used up by reacting with the dye.
This reaction has often lead to bleaches being stored in non coloured (white) portions of the tablets/pouches.
Despite the progress made in detergent composition stability, no one has yet come up with a way to provide a stable, dyed, bleach component in a detergent composition.
It is the object of this invention to solve this problem.